In a pigment having a fine particle diameter, since an aggregation force between pigment particles tends to be high, the pigment is liable to be insufficiently dispersed in a medium, such as an organic solvent or a molten resin. When the dispersibility of the pigment is insufficient, and the pigment is in an aggregated state, the coloring power thereof is liable to degrade.
In order to improve the dispersibility of pigment, various pigment dispersants and various pigment compositions each containing a pigment dispersant have been proposed.
For example, in order to improve the dispersibility of a yellow pigment in toner, a toner containing a polymer compound having a pyridone azo skeleton, a yellow pigment, and a binder resin has been proposed (PTL 1).
In addition, in order to improve the dispersibility of an azo pigment, an azo compound including a styrene/acrylic-based high molecular portion has also been proposed (PTL 2).
In addition, in order to improve the dispersibility of carbon black in toner, a technique in which a block copolymer or a graft copolymer, each of which is formed by polymerizing a styrene-based monomer and an acrylic acid ester-based monomer, is contained in a toner has been proposed (PTL 3).
In addition, a method has been proposed in which by the use of a specific high molecular dispersant and a magenta pigment in combination, the dispersibility thereof is enhanced, and coloring properties and charging properties of a toner are improved (PTL 4).
Furthermore, in order to disperse a phthalocyanine pigment in toner, a toner has been proposed which contains a polymer including sodium styrene sulfonate as a monomer unit, a phthalocyanine pigment, and a binder resin (PTL 5).